Hebgen Lake supports a diverse
aquatic ecosystem and is notable for its self-sustaining fish populations and unique ecological challenges. The lake is home to wild
rainbow and
brown trout, with studies showing that over 80% of rainbow trout are of wild origin.
Hatchery contributions are limited, helping to maintain a balanced and
resilient fish community. However, the presence of invasive species has raised management concerns. Harmful
algal blooms (HABs), particularly of
cyanobacteria such as
Anabaena flos-aquae, have occurred periodically in Hebgen Lake. These blooms can produce toxins that are dangerous to wildlife, livestock, pets, and humans. In response,
NorthWestern Energy developed a toxic algae monitoring and public notification plan to reduce health risks and improve lake safety. Groundwater inputs and
nutrient pollution are also ecological concerns. Advocacy groups have questioned the adequacy of environmental review for wastewater discharge permits in the area, citing potential risks to Hebgen Lake's
water quality. Historical water quality assessments conducted by the
Environmental Protection Agency in the 1970s provide baseline data on nutrient levels and other
limnological parameters, used to establish long-term ecological trends.
Fish Species Hebgen Lake supports a coldwater fishery dominated by trout species. Both native and introduced species are found in the lake. They benefit from its cool temperatures, and aquatic vegetation. Notably, wild
rainbow and
brown trout sustain popular recreational fisheries, while native species like mountain whitefish and westslope cutthroat trout contribute to ecological balance. The table below lists fish species documented in Hebgen Lake by Montana Fish, Wildlife & Parks. ==Recreation==